There are a significant number of commercial applications for lithium and lithium minerals and lithium salts (including the carbonate, hydroxide and halogenide salts) in various industries such as in the electronic, pharmaceutical, ceramic and lubricant industries, among others. Commercial applications include, but are not limited to, use in lithium batteries and reversible lithium ion batteries, use in lubricant greases, use as catalyst in the manufacture of synthetic rubber, use in the manufacture of glass and ceramics, use in the manufacture of television tubes, use in obtaining metal lithium, use as an air purifier in ventilation systems, use as a component of the electrolyte of accumulators used in submarines and telephone installations, use in power supplies for trains and telephones, use as starting material to obtain the isotope Li6, use in the control of gas moisture and air conditioning, use in heat absorption pumps, use in special welding and other fluxes, use in aluminum metallurgy and in the steel industry (for example for continuous casting and as cleaner/degreaser), use in the sterilization of water for swimming pools, and use in organic chemical synthesis as a reducing agent.
The key to performance of lithium and lithium compounds resides in obtaining high purity lithium metal or lithium compounds by minimizing impurities such as sodium, calcium and magnesium, carbonates, sulphates and borates that, while they do not significantly affect the purity of the lithium metal/compound produced, may impair performance.
Given the importance of lithium and its compounds, it is highly desirable to have a low impurity lithium source, and an economically viable method for the production of lithium and its compounds.
In this regard, a substantial portion of the lithium available at present is recovered from brines, which also contain high levels of sodium, making the production of lithium salts with low levels of sodium difficult and expensive.
Natural brines that contain lithium have many impurities as shown in Table 1 below.
TABLE 1Composition of natural brines expressed by weight percent.Great SaltSaltonSilverSalar deLakeSeaPeakAtacamaBrineBrineBrineBrineElementOceanUtahCaliforniaNevadaChileNa+1.057.05.716.27.175.70K+0.0380.41.420.81.851.71Mg++0.1230.80.0280.020.961.37Li+0.00010.0060.0220.020.150.193Ca++0.041.50.00.711.460.043Cl−1.914.015.0610.0616.0417.07Br−0.00650.00.00.0020.0050.005B0.00040.0070.0390.0050.040.04Li+/Mg++0.00080.00750.7861.00.1560.141Li+/K+0.00260.0150.01550.0160.0810.113Li+/Ca++0.00250.20.00081.04.840.244Li+/B0.250.8570.0514.03.754.83
Brine sources of lithium include the salars (brine deposits) in the Andes Mountains of South America which contain significant deposits of lithium salts; these include the Salar de Atacama, Chile, Salar de Uyuni, Bolivia, and Salar de Rincón, Province of Salta, Argentina.
Salars in the Andes Mountains are large, dry lakebeds where the brines are located just under a layer of crusted salt deposits. These types of deposits provide a viable source of concentrated natural brines which can potentially be treated to produce purified lithium salts, provided that impurities contained are in a ratio that allows the operation to be economically viable.
In these natural brines containing lithium, the impurities of the matrix, such as magnesium, calcium, sodium, sulphate and boron, must be minimized to obtain a lithium saline product suitable for a given use.
Alkaline metals, such as sodium, and alkaline earth metals, such as calcium and especially magnesium, must be substantially removed. To date, technical procedures to remove these impurities are not profitable.
The individual applications require that these ionic impurities are reduced to maximum specific levels and a number of processes have been described to remove such impurities.
For example, U.S. Pat. No. 4,207,297 describes an integrated continuous process for producing lithium hydroxide monohydrate and high purity lithium carbonate with a high average particle size, that comprises: converting technical grade impure lithium carbonate into lithium hydroxide by an alkalization step with a suspension of calcium hydroxide, separating the precipitated calcium carbonate of the resulting lithium hydroxide solution, dividing the resulting lithium hydroxide solution in two: a major portion and a minor portion at a ratio of volume of the major portion to the minor portion from about 10:1 to about 2:1, precipitating lithium hydroxide monohydrate from the major portion of the solution of lithium hydroxide and recovering the same, introducing carbon dioxide or lithium carbonate to the minor portion of the solution of lithium hydroxide for the additional precipitation of calcium as calcium carbonate, separating the calcium carbonate from the solution of lithium hydroxide, introducing carbon dioxide to the solution of lithium hydroxide to precipitate high purity lithium carbonate with high average particle size, separating the lithium carbonate from the resulting solution of diluted lithium carbonate and recycling the diluted solution of lithium carbonate to the step of alkalization
This process is hampered by extremely slow filtration, and is unsuitable for commercial practice.
U.S. Pat. No. 4,980,136 discloses a process for producing lithium chloride of a purity higher than 99%, and substantially free from boron, from a natural or waste brine of other processes that contains a sufficient amount of lithium substantially free from sulphate. This process comprises following the steps of contacting the brine containing lithium chloride that comprises from 2% to 7% by weight of lithium obtained by solar evaporation, by heating or any other conventional means, and being saturated with hydrated metal salts present in the brine and substantially free from free water, with an organic solution comprising from 5% to 40% by volume of a fatty alcohol that contains from 6 to 16 carbon atoms in kerosene in a volume ratio of organic solution to brine that ranges from about 1:1 to 5:1 to extract the boron from the brine to the phase of the organic solution; separating the phase of organic solution from the brine; evaporating the aqueous phase to a temperature higher than about 100.5° C. under vacuum of about 590 mm Hg to about 760 mm Hg to crystallize anhydrous lithium chloride; and separating the anhydrous lithium chloride from the remaining aqueous phase. Optionally, this process is followed by washing and/or extraction with a low molecular weight alcohol of the resulting lithium chloride to remove any residual boron together with other contaminants present below 1% in the lithium chloride, the lithium chloride being solubilised into the alcoholic solution. The alcohol solution containing lithium chloride is then filtered and evaporated to form lithium chloride crystals with a high purity of greater than 99.9%. The obtained anhydrous lithium chloride is particularly useful for producing lithium metal by electrolysis.
This process comprises extraction steps using a mixture of alcohol-kerosene solvents that are potentially not economically viable at the required industrial scale, even before considering the negative impact on the environment due to the use of alcohol-kerosene solvents.
U.S. Pat. No. 5,219,550 describes a process to produce lithium carbonate with a low content of boron from a natural brine containing lithium, comprising the steps of: contacting a brine containing lithium substantially free from sulphate, that has a lithium content from about 2% to about 7% by weight obtained by solar evaporation or other conventional means, the brine being saturated with hydrated metal salts present in the same and substantially free from free water, having a pH that ranges from about 1-2 measured when diluted with 10 volumes of water, with an organic solution comprising from about 5% to about 50% by volume of a fatty alcohol containing from 6 to 16 carbon atoms in kerosene in a volume ratio of organic solution to brine ranging from about 1:1 to 5:1, to extract the boron of the brine to the organic phase; separating the organic solution phase from the brine; removing magnesium and calcium from the brine by conventional means; adding sodium carbonate to precipitate the lithium carbonate from the brine; and separating the lithium carbonate resulting from the same. The lithium carbonate obtained is particularly useful for conversion thereof into high purity lithium chloride for the production of metal lithium by electrolysis.
This process involves multiple steps utilizing extraction with solvents and is not viable at industrial scale. It also has a negative impact on the environment.
As can be seen from the references described above, a significant research and development effort has been invested in the search for an economic means of industrial-scale exploitation of brine containing lithium and to produce lithium salts such as chloride and carbonate salts of sufficient purity to produce high-purity lithium metal.
To date, however, a process that allows treating a brine in an aqueous medium for obtaining high purity lithium carbonate without the use of extraction solvents, and easy to implement near salars has not been disclosed. Therefore, there remains a need for providing such a process.